Evolutionary biologists and geologists generally believe that a mass extinction of [[dinosaurs]] and other organisms happened 65 million years ago, the fifth mass extinction listed in geological history, at the end of the [[Cretaceous Period]]. Its primary cause is generally believed to be an asteroid or comet impact, linked to the Chicxulub crater off the Yucatan Peninsula of [[Mexico]], resulting in the extinction of 70% of all life on Earth.<ref>[http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Discovering_crater.html Chicxulub Impact Event: Discovering the Crater.] Accessed April 24, 2007.</ref> | Evolutionary biologists and geologists generally believe that a mass extinction of [[dinosaurs]] and other organisms happened 65 million years ago, the fifth mass extinction listed in geological history, at the end of the [[Cretaceous Period]]. Its primary cause is generally believed to be an asteroid or comet impact, linked to the Chicxulub crater off the Yucatan Peninsula of [[Mexico]], resulting in the extinction of 70% of all life on Earth.<ref>[http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Discovering_crater.html Chicxulub Impact Event: Discovering the Crater.] Accessed April 24, 2007.</ref> |